Method for the recording of sound



April ,1 B. E. G. MITTELL 1,855,981

METHOD FOR THE RECORDING OF SOUND Filed Jan. 19, 1926 2 Sheets-Sheet l 0 ENE Amp/lF/er Fly}.

@EIIE 3 April 26, 1932. B E G M EL 1,855,981

METHOD FOR THE RECORDING OF SOUND Filed Jan. 19, 1926 2 Sheets-Sheet 2 RAE 3maentor attorney "f records.

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Patented Apr. 26, 1932 UNITED STATES BRENGHLEY ERNEST GEORGE MITTELL, OF IVER, BUCKINGHAMSHIRE, ENGLAND, AS-

SIG-NOR, BY MESNE ASSIGNMENTS,

TO RADIO COBPOEATION OF AMERICA, OF

NEW YORK, N. Y., A CORPORATION OF DELAWARE 7 METHOD FOR THE RECORDING OF SOUND Application filed January 19, 1926, Serial No. 82,375, and in Great Britain February 18,1925.

This invention relates to improvements in methods for the recording of sound by electrical means.

According to the present invention the apparatus for the recording of sound comprises a device adapted to produce electrical oscillations corresponding to sound waves and the electrical oscillations are adapted to produce simultaneously a plurality of sound Suitable amplifying means may be provided, preferably of the thermionic type.

A number of separate recording instruments are preferably employed, each connected, electrically, with the microphone by a separate circuit, in such a manner that the electrical oscillations may receive in one circuit different treatment from that in another circuit. In one circuit, for example, all oscillations may receive additional amplification '0 or the oscillations of certain frequencies may wax, is that several records may be made simultaneously, in each of which some slight difference has been made in the amplitude or Wave form of the oscillations. In one the cutter may be adjusted for maximum volume, 5 in another the amplitude of the cut may be slightly reduced, in case the first mentioned should be found to cause a blast in reproduction, in another the higher frequency oscillations may be given additional amplifi- Corresponding variations may of course be made in records obtained by other processes than cutting on wax, for example by photographic means;

Another advantage of the invention, as applied to wax records, is that a record may be made on hard wax at the same time that I:

others are being made upon soft wax and the record on the hard Wax may be immediately played for the purpose of ascertaining, at once, whether the selection, for example, has been satisfactorily played.

Yet another advantage of the invention is that a number of similar originals may be produced simultaneously in order to increase the rate at which duplication and manufacture can be carried out.

The invention will now be described by way example with reference to the accompanying drawings wherein Figures 1, 2, 3 and 4 illustrate diagrammatically three alternative circuital arrangements according to the invention. a

In all the figures a microphone a which receives the sounds to be recorded is shown connected in series'with a battery and with the primary winding of a transformer b. The secondary winding of the transformer b is connected to a main amplifier c which is preferably of the thermionic type and may comprise any desired number of thermionic valves arranged in any known and suitable manner.

In Fig. 1 the output transformer from the main amplifier c has a single secondary winding having terminals d and e. Across the terminals 61 and e is connected an impedance f which acts as a potentiometer. The mid point 9 of the impedance is connected to one terminal of each of two recording devices it and 2' which may be of any known and suitable type. The other terminals of the recording devices are connected to contact arms j and 72 which are adapted to contact with various points along the potentiometer f through a number of impedances Z Z Z and m m m which areof such magnitude that the total impedance of the network to the right of points at and e, looked into from the points 03, e, is constant and equal to the impedance of the secondary winding which feeds it for all settings of the arms and 7c. The impedance of the network is moreover divided into two constant and equal halves at the point 9. The currents in the two recording devices it and 2' may thus be adjusted independently by means of the contact arms j and is without altering the total impedance of the network.

Fig. 2 shows a microphone a coupled by a transformer b to an amplifier 0 as in the previous example. The output transformer from the amplifier c is provided with two secondary windings n, 0 which may be connected directly with recording devices such as h and i or one or both may be connected. with a network such as that shown to the right of points d and e in Fig. 1. If for example it is desired to cut simultaneously two similar records, in order to increase the rate at which duplication can be effected, two similar recording devices may be connected to the secondary windings n and 0 and if one record is to be on soft wax (to be used for purposes of record manufacture) and another on hard wax for immediate reproduction to ascertain whether the recording has been satisfactorily carried out, two recording devices may be connected to the second ary windings n and 0 and, if necessary the damping of their armatures may be adjusted to compensate for the difference between the two waxes.

Fig. 3 shows an extension of the apparatus in Fig. 2. The microphone a, transformer Z) and amplifier c are connected as before and the secondary windings n and 0 of the output transformer are each connected to a further amplifier g0 and g respectively. The secondary windings n, 0, may either be connected with networks such as that shown to the right of point cl and e in Fig. 1, as shown in Fig. 4:, or alternatively one or both may be connected directly with a'recording device.

In any of the examples given a loud speaker may be connected in circuits in place of a recording device and so adjusted as to give a true indication of the quality and volume of the sounds which will eventually be delivered by the records made from the waxes which are being cut.

Although only one method of controlling the electrical oscillations has been described it must be understood that any known method of controlling the amplitude and wave form of electrical oscillations may be employed. Thus for example tappings may be taken from a choke coil or a resistance included in the output circuit of one of the valves of the amplifier. The above-mentioned tappings are connected either to the recording instrument or to the grid circuit of the next valve according to whether the transformer, choke or resistance is in the output circuitof the last valve of the amplifier or of an intermediate valve. The characteristics of the recording device may be adjusted during the recording process in any suitable manner, as for example, by varying the capacity effectively in shunt with the device.

When an electromagnetic recording instrument is used means may be provided to control the magnetic fiux which passes through the vibrating member. For example when electromagnets are employed the exciting current may be varied or a supplementary permanent magnet may be used so that its flux assists or opposes, to a greater or less extent, the flux produced by the electromagnet. If a permanent magnet is used, its position may be varied relative to the vibrating member or again a supplementary magnet may be employed. A further means of varying the strength of the magnetic field is to employ a variable magnetic shunt which is adapted to short circuit more or less of the fiux.

Electrical damping may also be varied, as for example by varying the amount of resistance in series with the recordinginstrument.

The invention is of course not confined to recording upon wax or to any particular form of recording device. Any known process for sound recording may be used within the scope of the present invention.

I claim:

1. Apparatus for the recording of sound comprising a member adapted to be vibrated by sound waves which it is desired to record, means cooperating with said member and adapted to generate electrical oscillations corresponding to said sound waves, a plurality of circuits one or more of which includes means adapted to modify independentlythe wave characteristics of said electrical oscillations during the recording operation, and means whereby said electrical oscillations are adapted to produce simultaneously a plurality of sound records.

2. Apparatus for the recording of sound comprising a device adapted to produce electrical oscillations corresponding tothe sound waves which impinge upon it, a main amplifier adapted to amplify said electrical oscillations, a plurality of subsidiary amplifiers connected in parallel to the output of the main amplifier, a sound recording device adapted to be operated by the electrical current output from each subsidiary amplifier, and means between said main amplifier and said recording devices adapted to modify independently the wave characteristics of the electrical oscillations delivered to one or more of said recording devices.

3. Apparatus for the recording of sound comprising a device adapted to produce electrical oscillations corresponding to the sound waves which impinge upon it, a main amplifier adapted to amplify said electrical oscillations, a plurality of subsidiary amplifiers connected in parallel to the output of the main amplifier, a sound recording device adapted to be operated by the electrical cur rent output from each subsidiary amplifier, and means adapted to adjust the amplification factor of one or more of said subsidiary amplifiers independently of the others dur ing the recording process.

4. Apparatus for the recording of sound, comprising a device adapted to produce electrical oscillations corresponding to the sound waves which fall upon it, a plurality of recording devices adapted to be simultaneously actuated by said electrical oscillations and means for adjusting the characteristics of one or more of said recording devices independently of the other recording devices during the recording process.

5. Apparatus for the recording of sound, comprising a device adapted to produce electrical oscillations corresponding to the sound waves which fall upon it, a thermionic amplifier adapted to amp ify said electrical oscillations, a plurality of recording devices adapted to be simultaneously actuated by the amplified electrical oscillations and means for adjusting the characteristics of one of said recording devices during the recording process the impedance of the output circuit of said amplifier being maintained substantially constant.

6. Apparatus for the recording of sound, comprising a device adapted to produce electrical oscillations corresponding to the sound waves which fall uon it, a thermionic amplifier adapted to amplify said electrical oscillations, a transformer comprising a primary winding and a secondary winding said primary winding being adapted to carry the amplified electrical oscillations, a plurality of recording devices adapted to be actuated by the electrical oscillations induced in said secondary winding and means for varying the current flowing through one of said recording devices while maintaining the impedance into which said secondary winding feeds, substantially constant.

7. Apparatus as claimed in claim 6, wherein the impedance into which said secondary winding feeds is maintained substantially equal to the impedance of said secondary winding itself.

8. Apparatus for the recording of sound comprising a member adapted to be vibrated by sound waves which it is desired to record, means cooperating with said member and adapted to generate electrical oscillations corresponding to said sound waves, means for amplifying said oscillations, an impedance connected across said amplifying means, a plurality of recorders connected across portions of said impedance, and means for varying the connection of said recorders to said impedance while maintaining constant the impedance into which said amplifying means feed.

9. Apparatus for the recording of sound comprising a member adapted to be vibrated by sound waves which it is desired to record, means cooperating with said member for generating electrical oscillations corresponding to said sound waves, means for amplifying said oscillations, an. impedance connected across said amplifying means, a plurality of recorders connected across different por tions of said impedance, means for varying the connections of said recorders to said impedance to vary the potentials applied to said recorders, and additional impedances connected to said first named impedance for maintaining constant the impedance into which said amplifying means feeds.

10. Apparatus for the recording of sound comprising a member adapted to be vibrated by sound waves which it is desired to record, means cooperating with said member for generating electrical oscillations corresponding to said sound waves, means for amplifying said oscillations, a plurality of subsidiary amplifying means connected in parallel to the output of said first amplifying means, an impedance connected across each of said subsidiary amplifying means, a plurality of recorders connected across portions of said impedances, and means for varying the connection of each of said recorders to said impedances while maintaining constant the im pedance into which each of said subsidiary amplifiers feeds.

11. Apparatus for the recording of sound comprising a member adapted to be vibrated by sound waves which it is desired to record, means cooperating with said member for generating electrical oscillations corresponding to said sound waves, means for amplifying said oscillations, a plurality of subsidiary amplifying means connected in parallel to the output of said first named amplifying means, an impedance connected across the output of each subsidiary amplifying means, a plurality of recorders connected across different portions of each impedance, means for varying the connections of said recorders to said impedances to vary the potentials applied to said recorders, and additional impedances connected to each of said first named impedances for maintaining constant the impedance into which each of said subsidiary amplifying means feeds.

12. The method of recording sound which consists in generating electrical oscillations corresponding to sound waves, amplifying said oscillations in a plurality of separate paths while individually controlling the characteristics of the oscillations in each path so as to produce currents of different wave form in different paths, and separately recording the amplified oscillations from each of said paths.

13. The method of recording a plurality of 7 records of different characteristics from a single sound source which Comprises generating electrical oscillations corresponding to sound Waves from said source, amplifying said osclllatlons, separatlng said osclllatlons in a plurality of paths, individually controlling the characteristics of the oscillations in each path so as to produce currents of different wave form in difi'erent paths, and separately recording the oscillations from each path.

In testimony whereof I have signed my name to this specification.

' BRENCHLEY ERNEST GEORGE MITTELL. 

